I haven't done sandbox detection for some years now, but around 2020, it was already "difficult" as in hard to write from scratch... yet already skid easy as in "copy+paste" from something that does it already. Surely newer sandboxes take more stuff into account, but at the same time more detection examples get published, simply advancing the starting point.
So maybe TikTok has a few people focused on it, possibly with some CI tests for several sandboxes. I don't think it's particularly hard to do 🤷